Dumbbell



FIG. 1 is a perspective view of a dumbbell showing my new design;

FIG. 2 is a top plan view thereof;

FIG. 3 is a side elevational view thereof;

FIG. 4 is a right end elevational view thereof;

FIG. 5 is a bottom plan view thereof; and,

FIG. 6 is a left end elevational view thereof.

The ornamental design for a dumbbell, as shown.